Immediate Goals: To examine the cardiovascular morbidity in children with obstructive sleep apnea (OSA). Career Development Goals: To provide sufficient time to develop a research training program in pediatric sleep medicine and build on the current patient-oriented research. Research Project: The project will test the hypothesis that children with OSA have baroreceptor dysfunction, which correlates with BP abnormalities, which in turn predict end organ injury in the form of an increase in left ventricular mass. The goal is to examine in children (1) the interaction between OSA and baroreflex dysfunction, (2) the relation of OSA severity and baroreflex dysfunction to abnormalities in blood pressure control during wakefulness and sleep, (3) the association of the diminished baroreflex gain and impaired blood pressure control with an index of end organ damage, the left ventricular mass index, and (4) whether effective treatment of OSA results in significant improvement in baroreceptor function, blood pressure control and a decrease in left ventricular mass index. We will accomplish these aims by studying 7-13 year-old children with OSA and a matched group of normal children in a cross-sectional design. Baroreceptor function, 24-hour ambulatory blood pressure and left ventricular mass index will be studied. Baroreceptor function will be measured by non-invasive techniques based on combined computer analysis of heart rate and blood pressure measured by portapres. 24-hour ambulatory blood pressure will be measured by a spacelab monitor, and left ventricular mass index will be measured by direct M-mode echocardiogram. In a longitudinal study, the effect of adequate treatment of OSA on baroreceptor function, daytime and nocturnal blood pressure and left ventricular mass index will be examined. A cohort of children with OSA and matched controls will be followed for a period of 12 months after treatment. (End of Abstract)